Nickel silver is resistant to corrosion. The zinc component should be sacrificial to both the nickel and copper components.
I’d be surprised if the black gunk that forms on the rails is nickel oxide. Under normal atmospheric conditions nickel doesn’t oxidize. Copper oxides are black to greenish (but, apparently, so is nickel oxide).
Using abrasive “erasers” on nickel silver is not going to cause any problems. You can tell by the deposits on the eraser that it is not removing or even scratching the nickel silver. The alloy is quite hard as well as resistant to corrosion.
Mind you, plain dry paper towel is perfectly adequate to remove the black gunk. It’s not bonded to the rail.
I find the dirtiest rails are places where wheelslip is common, somewhat paradoxically.
The “John Allen” track cleaning car is very simply a masonite (hardboard) pad that is mounted beneath a freight car. It has worked simply and reliably for 60+ years.
This is not mine, but a picture I found on line. Mine are packed away.
This should give you the basic idea.
A “John Allen” car will not clean track very well that is already dirty, but it is very good at keeping track clean and gleamed.
Other people have already replied to this one. I am a track gleamer, and only use kraft paper on a wood backer to hand clean my rails.
My layout had subways, mostly underground. I had liftoffs for access, but there were always places I couldn’t get to. The CMX car was always in my plans, and I have never regretted getting it. If you have inaccessible tunnels, you need a good track cleaning car.
Several years ago, I got to visit Gulliver’s Gate in NYC. It’s a 1:87 model of world scenes, with at least a loop of HO track and trains on every “continent.”
I noticed one anomaly. Although the appropriate national railroads were represented faithfully, I kept noticing a few CN and Rio Grande boxcars, everywhere. I finally chased down their “train guy,” who explained that they were Walthers track cleaning cars, which ran constantly to keep the track clean, but they hadn’t gotten around to repainting and re-decaling them yet. He was quite happy with the way they kept the track clean.
Sadly, Gulliver’s Gate couldn’t pay their sky high NYC rent and they shut down.
I built a variation on the “John Allen” masonite pad track cleaning car. I used an Athearn 40 foot boxcar for my track cleaning car. Instead of the usual pad of masonite, I used a rectangle of aluminum flat stock with the leading and trailing edges bent upward slightly. I glued the aluminum rectangle to the heads of the nails I used to locate the pad under the car. I next glued a piece of Fun Foam 2mm thick sheet foam to the aluminum pad (no more short across the rails). Using the points of the nails to mark their locations on the underside of the boxcar, I drilled holes slightly larger than the nail diameter to ensure the pad would stay aligned with the track but be allowed to “float” between the car and the track. Before replacing the body of the boxcar on the modified frame, I marked, drilled and press fit a block of hardwood to the top of the nails as weight to force the pad against the rails. The hardwood block is sized so as not to touch the body of the boxcar. I can run the car with the pad dry or apply a few drops of CRC 2-26 if I haven’t run the layout in a while. Maybe not quite as effective as a CRX car but a heck of a lot cheaper!
It appears that the Walthers track cleaning car uses springs between the cleaning pad and the underside of the car to keep the cleaning pad in contact with the rails. Unless the car is extra heavy, such springs could intefere with the cars normal tracking over the rails. That is the real beauty of the “John Allen” style car as the cleaning pad puts no more strain or tracking interference on the car itself beyond that of coupling another car or two to it.
In view of the recently published list, which is really about three years old already, and that kerosene came out on top as a fluid for keeping the rails clean and not interfering with running, why not use that on a disposable pad? It is the fluid of choice, is a distillate of sorts of oil, and it should both clean and maintain the surface of the rails.
